Question

A bag contains 2 blue marbles and 5 red marbles. You choose one marble and

without replacing it, youchoose a second marble. What is the probability of
choosing: A). A red marble first, then a blue marble second? B). A blue marble
GIVEN that a red marble was chosen first?

Answer 1

A) 5/7 and 2/6 B) 4/7

Explanation:

First find the total and then establish probability for each color: 2+5 = 7 total marbles.
`(2)/(7)` for blue and
`(5)/(7)` for red. Because you don't replace the marble you took out the total will do down one but the number of blue will not be affected to it just changed from
`(2)/(7) to (2)/(6)`

On part b I'm a little confused, are you putting a blue marble in the bag and then finding red's probability? If so, you are in theory replacing the first red marble so the total will be 7 again but since it's a blue marble your probabilities change to
`(3)/(7)` for blue and
`(4)/(7)` for red.